Binder compositions for textile sheet products are usually in aqueous form and by way of the binder component generally comprise polymers based on ethylenically unsaturated monomers. Said polymers typically comprise units of crosslinking monomers and therefore are capable of crosslinking with each other and optionally also with fibers and hence of contributing to the formation of textile sheet products of higher strength. This makes it possible to achieve durable fixation of the fibers and also an enhanced ability of the textile sheet products to resist mechanical loading, even on contact with liquids. The textile sheet products known as nonwovens are obtainable by the airlay, wetlay or spunlay process for example.
Polymers comprising N-methylolacrylamide (NMA) units, as described for example in U.S. Pat. No. 4,449,978, have hitherto dominated industrial practice in relation to binder components. Disadvantageously, polymers of this type crosslink with formaldehyde formation, which is deprecated for toxicological reasons. In addition, such polymers often already contain formaldehyde as a concomitant as a consequence of their method of making, for example the use in their polymerization of formaldehyde-releasing initiators, such as sodium formaldehydesulfoxylate (SFS). However, formaldehyde may also be imported through the addition of certain stabilizers.
There is accordingly a need to minimize the formaldehyde content of binder compositions and to provide ideally formaldehyde-free textile sheet products in an efficient manner. WO 2013/072713 proposes mixtures of carboxylic acid/anhydride modified polymers useful as binders. WO 2009/024216 recommends copolymers comprising specific sulfonic acid monomer units for use as binders for various applications. WO 2004/065437 relates to silicone-modified chain growth addition polymers. Proposals for use as binder component also include styrene-butyl acrylate polymers functionalized by, for example, interpolymerization with acrylamide, (meth)acrylic acid or hydroxyethyl acrylate, for example Primal™ NW-1845K. EP2199332 describes binder compositions comprising carboxyl-functionalized styrene-acrylate copolymers and polysaccharides, proteins or lignin/lignosulfonates. Textile sheet products obtained therewith, however, have low rates of wetting, minimal capacities for water absorption or long times to droplet penetration. Moreover, the drying/curing of binder compositions comprising styrene-butyl acrylate polymers requires higher temperatures in the manufacture of textile sheet products and so is more energy-intensive.
WO 2007/120341 and WO 99/52961 recommend the use of blocked polyisocyanates as binders for nonwovens. To cure the nonwovens, the isocyanates are deblocked by detaching the blocking groups, thus generating by-products, and this may for example entail an unwelcome odor nuisance.
In addition, prior art binder compositions that eschew formaldehyde-releasing polymers frequently lead to textile sheet products of insufficient strength, in particular insufficient wet tensile strength.